High-strength polyethylene fiber

ABSTRACT

A high strength polyethylene filament having tenacity of at least 15 cN/dTex, which comprises a polyethylene having a weight-average molecular weight of 300,000 or less and a ratio of a weight-average molecular weight to a number-average molecular weight (Mw/Mn) of 4.0 or less as determined in a state of the filament, and containing 0.01 to 3.0 branched chains per 1,000 backbone carbon atoms. When cut fibers are obtained by cutting the polyethylene filament, a rate of dispersion-defective fibers is 2.0% or less.

TECHNICAL FIELD

The present invention relates to a novel polyethylene filament with highstrength which can be applied to a wide range of industrial fields suchas high performance textiles for a variety of sports clothes,bulletproof or protective clothing, protective gloves, and-a variety ofsafety goods; a variety of ropes (tug rope, mooring rope, yacht rope,construction rope, etc.); fishing threads; braided ropes.(e.g., blindcable, etc.); nets (e.g., fishing nets, ground nets, etc.); reinforcingmaterials for chemical filters, battery separators, capacitors andnon-woven cloths; canvas for tents; reinforcing fibers for sports goods(e.g., helmets, skis, etc.), speaker cones and composites (e.g.,prepreg, etc.); and reinforcing fibers for concrete, etc.

BACKGROUND ART

As a polyethylene filament with high strength, there is known a filamentwhich is produced from an ultra-high molecular weight polyethylene by aso-called gel-spinning method and which has such a high strength andsuch a high elastic modulus that any of conventional filaments has neverpossessed, as disclosed in ,7P-B-60-47922, and this filament has alreadycome into industrially wide use.

JP-B-64-8732 discloses a filament which is made from an ultra-highmolecular weight polyethylene having a weight-average molecular weightof at least 600,000 as a starting material by so-called “gel spinningmethod” and which has a higher strength and a higher elastic modulusthan any of conventional filaments.

A high strength polyethylene filament produced by melt spinning isdisclosed in, for example, U.S. Pat. No. 4,228,118. According to thispatent, the high strength polyethylene filament disclosed is obtained byextruding a polyethylene having a number-average molecular weight of atleast 20,000 and a weight-average molecular weight of less than 125,000through a spinneret which is maintained at the temperature between 220and 335° C., then taking over the polymer at the rate of at least 30m/min. followed by drawing it at least 20 times at the temperaturebetween 115 and 132° C. Thus the filament has a tenacity of at least10.6cW/dTex.

Moreover, JP-A-08-504891 discloses a high strength polyethylene filamentwhich is produced by melt spinning polyethylene with high densitythrough a spinneret, cooling the filament coming out from the spinneret,and then drawing the obtained fiber at the temperature of 50-150 C.

Since a high strength polyethylene filament by gel spinning wasinvented, the filament has been used in all fields, and the physicalproperties required for the high strength polyethylene filament as a rawmaterial became still higher in recent years. In order to deal with awide range use, i.e. to satisfy the required performance whichaccompanies each use, it is required to fulfill simultaneously that inany monofilament fineness, a filament should excel in mechanicalstrength and an elastic modulus, the filament should be uniform, andalso there should be no fusion between each monofilament, etc. Forexample, as far as applications such as battery separators areconcerned, a high strength polyethylene filament with small single yarnfineness is desired. By contrast, for ropes or nets with which a fuzz, arubbing and the like (a so-called wear resistance) pose a problem, theone where single yarn fineness is to some extent thicker conversely isdesirable.

Although it is tried to produce a high strength polyethylene filament bythe so-called melt spinning, a high strength polyethylene filament whichsatisfies all the above-mentioned performances has not yet beenobtained. It is possible to obtain a high strength polyethylene filamentby using gel spinning on the other hand. However, due to the fact that ahigh strength polyethylene filament with a low monofilament finenessobtained with gel spinning had many fusions and press-stickings betweeneach monofilament, the fiber fused and stuck by pressure becamethickness nonuniformity to be a defect so that such a problem as adeterioration of the physical properties of a nonwoven fabric arose whenthis filament was used for a nonwoven fabric particularly with a lowweight (METSUKE). Moreover, when the apparent diameter of the filamentbecame thick caused by the filament fused and stuck by pressure, therewas a problem such that the retention of knot strength and loop strengthfalls.

The present inventors assume that the following are the causes for theforegoing problems. In the melt spinning, the polymer has manyintertwines of molecular chains therein, and therefore, the polymerextruded from a nozzle can not be sufficiently drawn. Further, it ispractically impossible to use for the reason of improving strength apolymer having such an ultra-high molecular weight of more than1,000,000 in the melt spinning because the melt viscosity of the polymeris too high. Therefore, the resultant filament has a low strength. Onthe other hand, there is a gel spinning method mentioned above where apolyethylene having an ultra-high molecular weight of more than1,000,000. However, this method has the following problems. The spinningand drawing tensions for obtaining a filament becomes higher, and theuse of a solvent for spinning and the drawing of a filament at atemperature higher than the melting point of the filament cause fusionsand press-stickings in the filaments. Thus, a desired filament having auniform fineness can not be obtained. Moreover, when gel spinning wasused, it was easy to produce the nonuniformity of fiber presumed tooriginate in spinning unstable phenomena, such as resonance, in thelongitudinal direction, and thus there was a problem in respect ofuniformity. The present inventors have succeeded in obtaining apolyethylene filament having a high strength which the melt spinning andthe gel spinning in the art could not achieve, and thus accomplished thepresent invention.

DISCLOSURE OF INVENTION

The present invention provides a high strength polyethylene filamenthaving a tenacity of at least 15 cN/dTex, which comprises a polyethylenehaving a weight-average molecular weight of 300,000 or less and a ratioof a weight-average molecular weight to a number-average molecularweight (Mw/Mn) of 4.0 or less as determined in a state of the filament,and containing 0.01 to 3.0 branched chains per 1,000 backbone carbonatoms.

The present invention also provides a high strength polyethylenefilament, wherein the branched chain is an alkyl group containing atleast 5 carbon atoms, wherein said filament has an elastic modulus of atleast 500 cN/dTex, or wherein a rate of dispersion-defective fibers cutfrom the filament is 2.0% or less.

The present invention is explained in full detail below.

In the process for producing a filament according to the presentinvention, it is necessary to employ a novel and deliberate process. Forexample, the following process is recommended; however, this processshould not be construed as limiting the scope of the present inventionin any way.

Polyethylene referred to in the context of the present invention is apolyethylene of which the repeating unit is substantially ethylene, orit may be copolymerized with a small amount of other monomer such as ana-olefin. Surprisingly, the following features are given to thisfilament when the branch with a long chain is introduced to some extentby using a-olefin. It was surprisingly found by the inventors thatpress-sticking which takes place with the pressure brought at the timeof cutting fibers could be reduced by making the main chain hold acertain amount of branches. The detailed reason may be assumed asfollows for example, although it is not certain. A high strengthpolyethylene filament is essentially hard to be cut since molecularchains are highly oriented and thus crystallized in the direction of afiber axis. When cutting such a high strength polyethylene filament,press-sticking of the filament tend to takes place since a pressure isbrought to the filament at the time of cutting. It is assumed that byputting the branch with a long chain to some extent to a main chain, notto mention the fiber itself becoming soft, the portion of the branchedchain becomes amorphous so that the pressure at the time of cutting isreduced and thus press-sticking at the time of a cutting decreases.However, if the quantity of long chain branch increases too much, itbecomes a defect and the strength of fiber falls. Therefore, it isdesirable that alkyl groups containing at least 5 carbon atoms arepresent as branched chains at a rate of 0.01 to 3.0 per 1,000 backbonecarbon atoms from a viewpoint of obtaining a filament with high strengthand a high elastic modulus. Preferably, the rate ranges from 0.05 to 2,more preferably from 0.1 to 1 per 1,000 backbone carbon atoms.

Also, it is important that the polyethylene in the state of a filamenthas a weight-average molecular weight of 300,000 or less, and that theratio of a weight-average molecular weight to a number-average molecularweight (Mw/Mn) becomes 4.0 or less. Preferably, it is important that aweight-average molecular weight in the state of filament is 250,000 orless, and that the ratio of a weight-average molecular weight to anumber-average molecular weight (Mw/Mn) becomes 3.5 or less. Still morepreferably, a weight-average molecular weight in the state of a filamentis 200,000 or less, and that the ratio of a weight-average molecularweight to a number-average molecular weight (Mw/Mn) becomes 3.0 or less.

When a polyethylene of a degree of polymerization with which aweight-average molecular weight of the polyethylene in the state of afilament exceeds 300,000 is used as a raw material, the melt viscositybecomes very high, and therefore, the melt molding thereof becomes veryhard. In addition, when the ratio of the weight-average molecular weightto the number-average molecular weight of the polyethylene in the stateof a filament is at least 4.0, this polyethylene filament is lower inthe largest draw ratio in drawing and also lower in strength, ascompared with a case using a polymer having the same weight-averagemolecular weight. The reasons therefor may be assumed that the molecularchain with long relaxing time can not be fully drawn in the drawing stepand finally breaks, and that its wider molecular weight distributionpermits the amount of a component with a lower molecular weight toincrease to thereby increase the number of the molecular ends, whichlowers the strength of the resultant filament, as compared with apolyethylene having the same weight-average molecular weight. Inaddition, the polymer may be intentionally deteriorated in the step ofmelt extrusion or spinning so as to control the molecular weight and themolecular weight distribution of the polyethylene in the state of afilament; or otherwise, a polyethylene having, a narrow molecular weightdistribution may be used.

In the method preferable for the present invention polyethylenementioned above is melt-extruded by an extruder, quantitativelydischarged through a spinneret with a gear pump. The resultantthreadlike polyethylene is then quenched with a cooled air, and drawn ata. predetermined speed. In the drawing step, it is important that thethreadlike polyethylene is drawn quickly enough. In other words, it isimportant that the ratio of the discharge linear speed to the windingspeed is at least 100, preferably at least 150, more preferably at least200. This ratio can be calculated from the diameter of the mouthpiece,the discharge amount from a single hole, the polymer density in themolten state, and the winding speed. Thus, since no solvent is used, theprocess of which is different from gel-spinning, when a round spinneretis used, the cross section of the filament becomes round in shape andthus press-sticking is hard to be generated even under a tension atspinning and drawing.

It is preferable to employ the drawing method further shown below forobtaining the filament according to the present invention in addition tothe above-mentioned spinning conditions.

Thus, it was found that the physical properties of a filament weresurprisingly improved by drawing the filament at a temperature which isless than the α-relaxation temperature of the filament, specificallyless than 65° C. and then further drawing at a temperature which ishigher than the α-relaxation temperature of the filament and lower thanthe melting point of the same filament, specifically more than 90° C.The generation of fusion and press-sticking of fiber is effectivelyprevented by drawing at a temperature which is lower than the meltingpoint of the filament. In this case the filament may be drawn further inmulti-stages.

In the present invention, a predetermined fiber was obtained by fixingthe speed of the first set of a godet roller with 5 m/min, whereasvarying the speed of the other godet rollers on the occasion of thedrawing process.

Hereinafter, the method of measurement and the measuring conditions forfinding the characteristic values according to the present invention areexplained below.

(Tenacity and Elastic Modulus)

The tenacity and the elastic modulus of a sample, of the presentinvention, with a length of 200 mm (the distance between each of chucks)were measured as follows. The sample was drawn at a drawing speed of100%/min., using “Tensilon” (Orientic Co., Ltd.). A strain-stress curvewas recorded under an atmosphere of a temperature of 20° C. and arelative humidity of 65%. The tenacity of the sample (cN/dTex) wascalculated from a stress at the breaking point of the curve, and theelastic modulus (cN/dTex) was calculated from a tangent line which showsthe largest gradient at or around the origin of the curve. Therespective values were measured 10 times, and the 10 measured valueswere averaged.

(Weight-Average Molecular Weight Mw, Number-Average Molecular Weight Mnand Ratio of Mw/Mn)

The values of the weight-average molecular weight Mw, the number-averagemolecular weight Mn, and the ratio of Mw/Mn were measured by gelpermeation chromatograph (GPC). As the apparatus for GPC, GPC 150CALC/GPC (manufactured by Waters) equipped with one column (GPC UT802.5manufactured by SHODEX) and two columns (UT806M) was used. As a solventfor use in measurement, o-dichlorobenzene was used, and the temperatureof the columns was set at 145° C. The concentration of the sample was1.0 mg/ml, and it was measured by injecting 200 μl of the sample. Thecalibration curve of the molecular weight was found by the universalcalibration method, using a polystyrene sample having a known molecularweight.

(Measurement of Branch)

The branch of an olefin polymer is determined by using 13 C-NMR (125MHz). The measurement was performed using Randall's method described inRev. Macromol. Chem. Phys., C29 (2&3), pp.285-297.

(Dynamic Viscoelasticity Measurement)

Dynamic viscosity measurement in the present invention was performedusing the “Reo-Vibron DDV-01PP type” (manufactured by Orientic Co.,Ltd.). Filaments are divided or doubled so as to become 100 deniers ±10deniers as a whole, with making the arrangement of each monofilament asuniformly as possible, both the ends of fiber being wrapped in aluminumfoil and pasted up by the cellulosic adhesive so that a measurementlength (distance between metallic chucks) may be set to 20 mm. Theoverlap width in this case may be about 5 mm in consideration offixation with metallic chucks. Each specimen was carefully installed tothe metallic chucks set as an initial width of 20 mm so that the fibermight not be slackened or twisted. This experiment was conducted aftergiving a preliminary modification for several seconds under thetemperature of 60° C., and the frequency of 110 Hz beforehand. In thisexperiment, temperature distribution was determined on the frequency of110 Hz from the low temperature side at the increasing rate of about 1°C./min. for the temperature span between −150° C. to 150° C. In themeasurement, a static load was set as 5 gf, and the automatic regulationof the sample length was carried out so that fiber might not slacken.The amplitude of dynamic modification was set as micrometers.

(Ratio of a discharge linear speed and a spinning speed (draft ratio))

A draft ratio (Ψ) is given by the following formula. Draft ratio (Ψ)=aspinning speed (Vs)/a discharge linear speed (V)

Best Mode for Carrying Out the Invention EXAMPLE 1

A high density polyethylene which had a weight-average molecular weightof 115,000 and a ratio of the weight-average molecular weight to anumber-average molecular weight of 2.3 and contained branched chainswith at least 5 carbon atoms in a number of 0.4 per 1,000 backbonecarbon atoms was extruded through a spinneret having 30 holes withdiameters of 0.8 mm so that the polyethylene could be discharged at 290°C. and at a rate of 0.5 g/min. per hole. The threadlike polyethyleneextruded is allowed to pass through a thermally insulating zone with alength of 15 cm and then quenched at 20° C. and 0.5 m/s, and wound up ata speed of 300 m/min. This non-drawn filament was drawn with at leasttwo sets of temperature controllable Nelson rollers. The drawing in thefirst stage was carried out at 25° C. to a length 2.8 times longer. Thefilament was further heated to 115° C. and was drawn to a length seventimes longer. The physical properties of the resultant drawn filamentare shown in Table 1.

EXAMPLE 2

The drawn filament of Example 1 was heated to 125° C. and was drawn to alength 1.3 times longer. The physical properties of the resultantfilament are shown in Table 1.

EXAMPLE 3

A drawn filament was produced substantially in the same manner as inExample 1, except that the drawing temperature in the first stage waschanged to 40° C. The physical properties of the resultant filament areshown in Table 1.

EXAMPLE 4

A drawn filament was produced substantially in the same manner as inExample 1, except that the drawing temperature in the first stage waschanged to 10° C. The physical properties of the resultant filament areshown in Table 1.

EXAMPLE 5

A drawn filament was obtained substantially in the same manner as inExample 1, except that a high density polyethylene having aweight-average molecular weight of 152,000 and a ratio of theweight-average molecular weight to a number-average molecular weight of2.4 and contained branched chains with at least 5 carbon atoms in anumber of 0.4 per 1,000 backbone carbon atoms was extruded at 300° C.through a spinneret having 30 holes with diameters of 0.9 mm so that thepolyethylene could be discharged at 0.3 g/min. per hole. The physicalproperties of the resultant filament are shown in Table 1.

EXAMPLE 6

A high density polyethylene which had a weight-average molecular weightof 175,000 and a ratio of the weight-average molecular weight to anumber-average molecular weight of 2.4 and contained branched chainswith at least 5 carbon atoms in a number of 0.4 per 1,000 backbonecarbon atoms was extruded through a spinneret having 30 holes withdiameters of 1.0 mm so that the polyethylene could be discharged at 300°C. and at a rate of 0:8 g/min. per hole. The threadlike polyethyleneextruded is allowed to pass through a thermally insulating zone with alength of 15 cm and then quenched at 20° C. and 0.5 m/s, and wound up ata speed of 150 m/min. This non-drawn filament was drawn with at leasttwo sets of temperature controllable Nelson rollers. The drawing in thefirst stage was carried out at 25° C. to a length 2.0 times longer. Thefilament was further heated to 115° C. and was drawn to a length 4.0times longer. The physical properties of the resultant drawn filamentare shown in Table 1.

COMPARATIVE EXAMPLE 1

A drawn filament was produced substantially in the same manner as inExample 1, except that the drawing temperature at the first stage waschanged to 90° C. The physical properties of the resultant filament areshown in Table 2.

COMPARATIVE EXAMPLE 2

A drawn filament was produced substantially in the same manner as inExample 1, except that the spinning speed was changed to 60 m/min, thedrawing temperature in the first stage was changed to 90° C., the drawratio at the first and the second stage were changed to 3.0 and 7.0respectively. The physical properties of the resultant filament areshown in Table 2.

COMPARATIVE EXAMPLE 3

A drawn filament was produced substantially in the same manner as inExample 1, except that the spinning speed was changed to 60 m/min, thedrawing temperature at the first stage was changed to 63° C., the drawratio at the first and the second stage were changed to 3.0 and 7.0respectively. The physical properties of the resultant filament areshown in Table 2.

COMPARATIVE EXAMPLE 4

A drawn filament was obtained substantially in the same manner as inExample 1, except that a high density polyethylene having aweight-average molecular weight of 123,000 and a ratio of theweight-average molecular weight to a number-average molecular weight of2.5 and contained branched chains with at least 5 carbon atoms in anumber of 12 per 1,000 backbone carbon atoms was used. However, thefilament was frequently broken during the drawing and only a filamentdrawn with a lower draw ratio was obtained. The physical properties ofthe resultant filament are shown in Table 2.

COMPARATIVE EXAMPLE 5

A non-drawn filament was obtained substantially in the same manner as inExample 1, except that a high density polyethylene having aweight-average molecular weight of 121,500 and a ratio of theweight-average molecular weight to a number-average molecular weight of5.1 and contained branched chains with at least 5 carbon atoms in anumber of 0.4 per 1,000 backbone carbon atoms was extruded through aspinneret having 30 holes with diameters of 0.8 mm so that thepolyethylene could be discharged at 270° C. and at a rate of 0.5 g/min.per hole. This non-drawn filament was drawn at 90° C. to a length 2.8times longer. After that, the filament was further heated to 115° C. andwas drawn to a length 3.8 times longer. The physical properties of theresultant drawn filament are shown in Table 2.

COMPARATIVE EXAMPLE 6

The non-drawn filament obtained in Comparative Example 4 was drawn at40° C. to a length 2.8 times longer. After that, the filament wasfurther heated to 115° C. and was drawn to a length 4.0 times longer.The physical properties of the resultant drawn filament are shown inTable 2.

COMPARATIVE EXAMPLE 7

A non-drawn filament was produced substantially in the same manner as inExample 1, except that the spinning speed was changed to 80 m/min. Thisnon-drawn filament was drawn at 80° C. to a length 2.8 times longer.After that, the filament was further heated to 115° C. and was drawn toa length 4.0 times longer. The physical properties of the resultantdrawn filament are shown in Table 3.

COMPARATIVE EXAMPLE 8

A non-drawn filament was obtained substantially in the same manner as inExample 1, except that a high density polyethylene having aweight-average molecular weight of 123,000 and a ratio of theweight-average molecular weight to a number-average molecular weight of6.0 and contained branched chains with at least 5 carbon atoms in anumber of 0 per 1,000 backbone carbon atoms was extruded through aspinneret having 30 holes with diameters of 0.8 mm so that thepolyethylene could be discharged at 295° C. and at a rate of 0.5 g/min.per hole. This non-drawn filament was drawn at 90° C. to a length 2.8times longer. After that, the filament was further heated to 115° C. andwas drawn to a length 3.7 times longer. The physical properties of theresultant drawn filament are shown in Table 3.

COMPARATIVE EXAMPLE 9

A non-drawn filament was obtained substantially in the same manner as inExample 1, except that a high density polyethylene having aweight-average molecular weight of 52,000 and a ratio of theweight-average molecular weight to a number-average molecular weight of2.3 and contained branched chains with at least 5 carbon atoms in anumber of 0.6 per 1,000 backbone carbon atoms was extruded through aspinneret having 30 holes with diameters of 0.8 mm so that thepolyethylene could be discharged at 255° C. and at a rate of 0.5 g/min.per hole. This non-drawn filament was drawn at 40° C. to a length 2.8times longer. After that, the filament was further heated to 100° C. andwas drawn to a length 5.0 times longer. The physical properties of theresultant drawn filament are shown in Table 3.

COMPARATIVE EXAMPLE 10

A spinning was conducted by using a high density polyethylene having aweight-average molecular weight of 820,000 and a ratio of theweight-average molecular weight to a number-average molecular weight of2.5 and contained branched chains with at least 5 carbon atoms in anumber of 1.3 per 1,000 backbone carbon atoms. However, the meltviscosity of the polymer was too high and the polymer could not beextruded uniformly.

COMPARATIVE EXAMPLE 11

A slurry-like mixture of an ultra-high molecular weight polyethylenehaving a weight-average molecular weight of 3,200,000 and a ratio of theweight-average molecular weight to a number-average molecular weight of6.3 (10 wt.%) and decahydronaphthalene (90 wt.%) was dispersed anddissolved with a screw type kneader set at 230° C., and was fed to amouthpiece which had 2000 holes with diameters of 0.2 mm and was set at170° C., using a weighing pump, so that the polyethylene could bedischarged at 0.08 g/min. per hole. A nitrogen gas adjusted to 100° C.was fed at a rate of 1.2 m/min. from a slit-like gas-feeding orificearranged just below a nozzle, and such a nitrogen gas was blown againstthe filament as uniformly as possible so as to evaporate off decalinfrom the surface of the non-drawn filament. Immediately after that, thenon-drawn filament was substantially cooled with the airflow set at 30degrees. The non-drawn filament was drawn at a rate of 50 m/min. withNelson-like-arranged rollers which were set on the side of downstreamfrom the nozzle. At this stage, the solvent contained in the filamentwas reduced to about half of the original weight. The resultant filamentwas subsequently drawn to a length 3 times longer, in an oven set at100° C. The filament was, subsequently drawn to a length 4.6 timeslonger, in an oven heated to 149° C. The resultant filament was uniformand it could be obtained without any breakage. The physical propertiesof the resultant filament are shown in Table 3.

COMPARATIVE EXAMPLE 12

The slurry-like mixture prepared substantially in the same manner as inComparative Example 11 was dissolved with a screw type kneader set at230° C., and was fed to a mouthpiece which had 500 holes with diametersof 0.8 mm and was set at 180° C., using a weighing pump, so that thepolyethylene could be discharged at 1.6. g/min. per hole. A nitrogen gasadjusted to 100° C. was fed at a rate of 1.2 m/min. from a slit-likegas-feeding orifice arranged just below a nozzle, and such a nitrogengas was blown against the filament as uniformly as possible so as toevaporate off decalin from the surface of the non-drawn filament. Afterthat, the non-drawn filament was drawn at a rate of 100 m/min. withNelson-like-arranged rollers which were set on the side of downstreamfrom the nozzle. At this stage, the solvent contained in the filamentwas reduced to about 60 wt. % of the original weight. The resultantfilament was subsequently drawn to a length 4.0 times longer, in an ovenset at 130° C. The filament was subsequently drawn to a length 3.5 timeslonger, in an oven heated to 149° C. The resultant filament was uniformand it could be obtained without any breakage. The physical propertiesof the resultant filament are shown in Table 3. TABLE 1 Example 1Example 2 Example 3 Example 4 Example 5 Example 6 Weight-Average g/mol115000 115000 115000 115000 152000 175000 Molecular Weight (polymer)Mw/Mn (polymer) — 2.3 2.3 2.3 2.3 2.4 2.4 Branched chains /per 0.4 0.40.4 0.4 0.8 0.4 containing at 1,000 least 5 carbon carbon atoms atomsDischarge rate per g/min 0.5 0.5 0.5 0.5 0.3 1.2 hole Spinning speedm/min 300 300 300 300 200 150 Draft ratio — 225 225 225 225 316α-relaxation ° C. 63 63 63 63 67 65 temperature Drawing ° C. 25 25 40 1025 25 temperature in the 1^(st) stage Draw ratio in the — 2.8 2.8 2.82.8 2.4 2.0 1^(st) stage Drawing ° C. 115 115 115 115 115 115temperature in the 2^(nd) stage Draw ratio in the — 5.0 5.0 5.0 5.0 4.84.0 2^(nd) stage Drawing ° C. 125 temperature in the 3^(rd) stage Drawratio in the — 1.2 3rd stage Draw ratio in — 14.0 16.8 14.0 14.0 11.58.0 total Weight Average g/mol 110000 110000 110000 110000 138000 138000Molecular Weight (filament) Mw/Mn (filament) 2.2 2.2 2.2 2.2 2.3 2.3Fineness dTex 36 30 36 36 65 302 Tenacity cN/dTex 18.2 19.1 17.9 18.718.9 15.1 Elastic modulus cN/dTex 820 880 801 871 820 401 Rate of % 1.0or 1.0 or 1.0 or 1.0 or 1.0 or 1.0 or dispersion- less less less lessless less defective fibers

TABLE 2 Comp. Comp. Comp. Comp. Comp. Comp. Ex. 1 Ex. 2 Ex. 3 Ex. 4 Ex.5 Ex. 6 Weight-Average g/mol 115000 115000 115000 123000 121500 121500Molecular Weight (polymer) Mw/Mn (polymer) — 2.3 2.3 2.3 2.5 5.1 5.1Branched chains /per 0.4 0.4 0.4 12 0.8 0.4 containing at 1,000 least 5carbon carbon atoms atoms Discharge rate per g/min 0.5 0.5 0.5 0.5 0.31.2 hole Spinning speed m/min 300 60 60 300 300 300 Draft ratio — 225 4545 225 225 225 α-relaxation ° C. 63 56 56 57 64 64 temperature Drawing °C. 90 90 63 25 90 40 temperature in the 1^(st) stage Draw ratio in the —2.8 3.0 3.0 2.0 2.8 2.8 1^(st) stage Drawing ° C. 115 115 115 115 115115 temperature in the 2^(nd) stage Draw ratio in the — 5.0 7.0 7.0 4.13.8 4.0 2^(nd) stage Draw ratio in — 14.0 21.0 21.0 8.2 10.6 11.2 totalWeight Average g/mol 110000 110000 110000 116000 116000 116000 MolecularWeight (filament) Mw/Mn (filament) 2.2 2.2 2.2 2.4 4.8 4.8 Fineness dTex36 119 119 61 47 45 Tenacity cN/dTex 14.0 12.1 13.1 14.2 13.1 13.4Elastic modulus cN/dTex 620 320 380 471 433 440 Rate of % 1.0 or 1.0 or1.0 or 1.0 or 1.0 or 1.0 or dispersion- less less less less less lessdefective fibers

TABLE 3 Comp. Comp. Comp. Comp. Comp. Comp. Ex. 7 Ex. 8 Ex. 9 Ex. 10 Ex.11 Ex. 12 Weight-Average g/mol 121500 123000 52000 820000 32000003200000 Molecular Weight (polymer) Mw/Mn (polymer) — 5.1 6.1 2.3 2.5 6.36.3 Branched chains /per 0.4 0 0.6 1.3 0 0 containing at 1,000 least 5carbon carbon atoms atoms Discharge rate per g/min 0.5 0.5 0.5 0.08 1.6hole Spinning speed m/min 80 300 300 50 100 Draft ratio — 60 225 22518.3 29.2 α-relaxation ° C. 57 64 54 82 89 temperature Drawing ° C. 8090 40 100 130 temperature in the 1^(st) stage Draw ratio in the — 2.82.8 2.8 3.0 4.0 1^(st) stage Drawing ° C. 115 115 100 149 149temperature in the 2^(nd) stage Draw ratio in the — 4.0 3.7 5.0 4.6 3.52^(nd) stage Draw ratio in — 11.2 10.4 14.0 13.8 14.0 total WeightAverage g/mol 116000 116000 50000 2500000 2650000 Molecular Weight(filament) Mw/Mn (filament) 4.8 4.8 2.2 5.1 5.3 Fineness dTex 167 48 36209 574 Tenacity cN/dTex 10.1 12.8 9.4 27.5 30.1 Elastic modulus cN/dTex280 401 301 921 1001 Rate of % 1.0 or 1.0 or 1.0 or 12.1 8.0 dispersion-less less less defective fibers

Industrial Applicability

There can be provided a high strength polyethylene filament which isexcellent in Tenacity and elastic modulus in any fineness ofmonofilament and has uniformity, the filament being free of fusion andpress-sticking between each monofilament in addition.

1. A high strength polyethylene filament having a tenacity of at least15 cN/dTex, which comprises a polyethylene having a weight-averagemolecular weight of 300,000 or less and a ratio of a weight-averagemolecular weight to a number-average molecular weight (Mw/Mn) of 4.0 orless as determined in a state of the filament, and containing 0.01 to3.0 branched chains per 1,000 backbone carbon atoms.
 2. A high strengthpolyethylene filament according to claim 1, wherein the branched chainscontain at least 5 carbon atoms.
 3. A high strength polyethylenefilament according to claim 1 or 2, wherein said filament has an elasticmodulus of at least 500 cN/dTex.
 4. A high strength polyethylenefilament according to any one of claims 1 to 3, wherein a rate ofdispersion-defective fibers cut from the filament is 2.0% or less.